Infant phonation research has focused on how infants use laryngeal and articulatory modification to produce speech, but made little reference to how the respiratory system underlies speech production. At the same time, infant respiration research has not linked breathing patterns to distinct phonatory behaviors or to the acoustic parameters that describe them. This application is a dissertation study that proposes to bridge this gap. The study's first specific aim is to measure infants' vocalizations and respiratory movements during the first year of life. Its second specific aim is to measure the degree to which the infants' laryngeal and respiratory behaviors are altered by both familiar and unfamiliar communicative partners. Infants will be studied during face-to-face dialogue and interactive play. This study will apply new instrumentation and analysis techniques to help offset the negative effects of noise and interference that have constrained signal acquisition in infant research. The goal of the study is to develop an explanatory model of the actions and reactions of normally developing infants engaged in communicative interaction, which in turn may lead to insights related to the identification and diagnosis of infants at risk for communicative impairments. [unreadable] [unreadable] [unreadable]